2 IO 



NATURE 



\jfune 29, 



observed to rise. Later on the scene changed to a landscape, 

 the vessels now taking the form of islands in the lake, covered 

 with more or less vegetation, and at last the mirage dissolved 

 itself in a haze. The phenomenon, which lasted from 4 to 7 

 o'clock p.m., is said to have furnished a most magnificent 

 spectacle. 



The additions to the Zoological Society's Gardens during the 

 past week include a Yellow Baboon (Cynocephalus babotiin °i 

 from West Africa, presented by Mr. A. Collison ; a Slender 

 Loris (Loris gracilis 6 ) from Ceylon, presented by Mrs. A. H. 

 Jamrach ; a Vulpine Phalanger (Phalangista vulpina) from 

 Australia, presented by Mr. E. Meek ; a Burmese Tortoise 

 ( Testitdo elongata) from the Western Dooars of Bhotan, pre ■ 



seated by Mr. B. H. Carew ; a Tree Snake (Ahatulla 



liocercus) from Pernambuco, presented by Mr. C. A. Craven ; a 

 Common Adder ( Vipera bents), British, presented by Mr. F. W. 

 Elliott ; a Rude Fox (Cam's rndis), a Common Rhea (Rhea 

 anuricana) from South America, deposited ; a Yellow Baboon 

 (Cynocephalus babonin) from West Africa, received on approval ; 

 a Burrhel Wild Sheep (Ovis burrhel), born in the Gardens, eight 

 Summer Ducks (Aix sfonsa), six Swinhoe's Pheasants (Euplo- 

 catnus swinhoii), bred in the Gardens. The following insects 

 having emerged during the past week : — Silk Moths : Aetias 

 selene, Samia cecropia, Attacus mylitttr; Moths : Hypocht 

 Deiltphila euphorbia, Deilephda vesperlilis, Trochilmm apiformis, 

 Sciapteron tabaniformis, Sesia musttifortnis, Callinwrphi domi- 

 nit/a : Butterflies : Apatitra iris, Vanessa xanthomelas, Vanessa 

 urticce, Aporia crabirgi. 



OUR ASTRONOMICAL COLUMN 



Maskelyne's Value of the Solar Parallax. — Mr. 

 Dunkin has consulted the first edition of Vince's " System of 

 Astronomy," published in 1797, and finds therein Maskelyne's 

 article on a new method of determining the solar parallax, the 

 same as in the second edition which appeared in 1814. 



Mr. W. J. Davies, writing from Tyglyn, Cilian Aeron, Car- 

 digan, asks, with reference to this value of the parallax, Is it 

 not probable that this was first published in the Philosophical 

 Transactions? Prof. Ball, in his " Elements of Astronomy" 

 (Longmans, 18S0), page 361, gives the value S"'723, and the 

 authority for it, viz., Phil. Trans., vol. lxi. p. 574, year 1 77 1 . 

 O.i this point we may remark that Prof. Ball, according to the 

 statement in his preface, has mainly relied for his numerical 

 data upon Houzeau's "Repertoire des Constantes Astrono- 

 miques " — a work which, though excellently designed, would, 

 according to our experience of it, benefit by a careful revision. 

 There are a number of errors in the first edition, which are 

 likely to be copied into more popular works, unless attention he 

 drawn to them. In the present case, where reference is made 

 for Maskelyne's parallax to the Phil. Trans., 1771, p. 574, we 

 find at that page a paper by Dr. Hornsby, entitled " The Quan- 

 tity of the Sun's Parallax as deduced from the Observation of 

 the Transit of Venus, on June 3, 1769, by Thomas Hornsby, 

 M.A., Savilian Professor of Astronomy in the University of 

 Oxford, and F.R.S.," in which the parallax from a number of 

 combinations is found to be S"'7S. Maskelyne's name is not 

 mentioned in the paper, which appears to relate exclusively to 

 Hornsby's own deductions. 



Mr. Dunkin having traced the publication of Maskelyne's note 

 to 1 797, the only earlier work of Vince in which it would be 

 likely to be found, is the first edition of his text-book, the 

 "Elements of Astronomy," 1790. Mr. Davies remarks that 

 Olinthus Gregory, in his "Treatise on Astronomy," published 

 in 1S03, refers to Maskelyne's method, and considered it the 

 best that had been given; he explains it almost in the same 

 words as in Vince, adding that the assumed value S"'S3 was 

 taken " agreeably to the result of observations on the transit in 

 1761." 



The Comet of May 17. — M. Trepied, in an account of his 

 observations made in Egypt during the total solar eclipse of 

 May 17, which was couimunicatcd to the Academy of Sciences 

 on the 19th inst., has the following interesting note : — "Vers le 

 milieu de la totalite, j'apercus a droite du Soleil, par un angle 



zenith de environ 90 , un trait legerement courbe vers le bas, 

 d'un eftet singulier, et en discordance evidente avecle reste de la 

 couronne. Je n'ai pas eu un seul instant l'idee que ce pouvait 

 etre une comete ; je n'en ai reconnu la nature qu' vine heure 

 apres l'eclipse, en comparant mon croquis a l'une des photo- 

 graphies obtenues par le Dr. Schuster. Cette photographie 

 montrait nettement le noyau a une distance du bord du Soleil un 

 peu superieure au diametre de cet astre ; Tangle zenith et la 

 direction de la queue s'accordaient bien avec ce que j'avais 

 dessine, mais j'avais arrete le trait a une distance beaucoup trop 

 faible du bord. Je n'ai pas cru cependant qu'il me fut permis de 

 rien changer a mon dessin." The sketch referred to is copied in 

 the Comptes rendus of the above sitting of the Academy. M. 

 Trepied further remarks : " L'eclat de la comete m'a paru du 

 nieme ordre que celui des parties exterieures de la couronne." 

 The position of the observing station, as provisionally deter- 

 mined by M. Trepied, is in longitude ih. 57m. 40s. east of 

 Paris, and latitude 26° 33' 21", where the middle of totality 

 occurred at 8h. 31m. 53s. a.m. local mean time. M. Trepied 

 says in the week following the eclipse he searched for the comet 

 many times before sunrise and after sunset, but without 

 detecting it. 



The comet has doubtless been sought for elsewhere, though 

 unfortunately without success. The object notified as having 

 become visible some ten days sjuce in the Cape Colony, near 

 the sun in the evenings, would be the comet 1S82 a (Wells), 

 March 17). 



Daylight Observation of Comet 1882 a. — rrof. Julius 

 Schmidt writes to the Astronomische Nachriehten that on June 

 10 after 3 p.m., in an exceptionally clear sky at Athens, he 

 observed the comet, though with difficulty, in the 6-feet refractor 

 of that observatory. By ten observations (the instrumental 

 corrections from previous determination) the approximate position 

 was found to be — 



h. m. h. m. s. 



June 10, at 3 597 M.T. Athens, R.A. 5 o 40, Deck + 23 19-4. 



This place differs from that inferred from the last orbit given 

 in this column (on observations to May 21) by - S''S in R.A. 

 and +3'. 2 in declination. The comet's distance from the nearest 

 limb of the sun was about 2° '8. 



PHYSICAL NOTES 



Professors Bellati and Naccari, of the University of 

 Padua, have recently sent to the Academy of Sciences at Turin, 

 a memoir on the heat developed in solid and liquid dielectrics 

 by successive electrostatic polarisations. They find that when 

 a dielectric, placed between two metal armatures, is subjected to 

 successive polarisations by means of a Ruhmkorff's coil, the 

 dielectric is warmed. This result had already been obtained by 

 Siemens and Righi in the case of glass ; the authors of the 

 memoir have experimented also on liquid dielectrics. They 

 have employed two methods : in one of these the heating was 

 indicated by the dilatation of the liquid dielectric (or, in the case 

 of a solid dielectric, of another liquid) observed in a capillary 

 tube. In the other method, the liquid dielectric was contained 

 in a glass vessel, in which were two concentric metallic cylinders 

 serving as the armatures of a' condenser. The outer one of 

 these two cylinders was open above and below ; the other was 

 closed, and communicated with a horizontal capillary tube con- 

 taining benzine. This cylinder, therefore, acted as the bulb of 

 an air-thermometer, the heating of the dielectric being indicated 

 by the displacement of the benzine in the capillary tube. This 

 phenomenon must not be confounded with the electric expansion 

 discovered by Fontana more than a century ago, and more 

 recently studied by Govi, Duter, and Quincke. The true elec- 

 tric expansion is instantaneous, and ceases when the polarisation 

 cea: es ; but the expansion due to the heat developed in the 

 dielectric by tepeated charges and discharges is progressive, and 

 increases by prolonging the action of the induction coil. Pro- 

 fessors Bellan and Naccari found no electrolytic decomposition 

 in the dielectric, nor was the heating due to the passage of a 

 feeble current through the dielectric. 



The utilisation of the earth's internal heat is a subject which 

 is attracting the attention of scientific men in Japan just now. 

 At a recent meeting of the Seismological Society, Mr. Milne 

 introduced the subject for the consideration of the members. He 

 first drew attention to the fact that philosophers have told us the 

 whole available energvupon the surface of the earth had in some 



